In fact, just the opposite was true in 93 women studied at Ohio State University Medical Center. Women who were sexually active in the final three weeks of their pregnancies carried their babies an average of 39.9 weeks, compared to average delivery at 39.3 weeks among women who abstained from sexual activity at term.
"Patients may continue to hear the 'old wives' tale' that intercourse will hasten labor, but according to this data, they should not hear it from the medical community," concludes Dr. Jonathan Schaffir, an obstetrician at OSU Medical Center and author of the study published in the June issue of the journal Obstetrics & Gynecology.
Schaffir also said the data don't support a recommendation to engage in sexual activity, either.
Of the 93 women enrolled, 47, or 50.5 percent, reported they had sex during the final weeks of their pregnancies - more than any other similar study has indicated.
The participating women were those with low-risk single pregnancies enrolled at their doctor's office visit after the 37th week of pregnancy. At this and subsequent routine visits, patients were asked whether they had engaged in sexual intercourse during the preceding week and if so, how many times. Cervical examinations also were performed at each visit to gauge whether the sexual activity had a "ripening" effect on the cervix.
Schaffir found no correlation between the frequency of sexual intercourse and the score assigned to measure the cervix. That lack of change in the cervix among sexually active women, combined with the lack of difference in delivery dates among the two groups, suggests that sexual intercourse has no effect on inducing labor, Schaffir said.
He acknowledged that women who are more comfortable late in pregnancy may be more likely to engage in sexual activity, and that women who experience abdominal discomfort or pelvic pressure - possible signs of earlier delivery - won't be inclined to want to have sex. Schaffir also said that because of the highly personal nature of sexual behavior, the study does not address specific components of sexual behavior that might have varying effects on the onset of labor.
The study was conducted at OSU Medical Center between July 2004 and July 2005. The two groups of women did not differ significantly in terms of age, weight and previous pregnancies.